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LCARP White Paper rev02_2019_02_04_CLEAN.docx

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Low Charge Ammonia Packaged Refrigeration Systems: Achieving Ultra-Reliable Operation

Trevor Hegg(a), Kurt Liebendorfer(a), Don Hamilton(a), Jake Denison(a), (a) Evapco, Inc.

Taneytown, MD

Introduction

The refrigeration industry has been migrating to natural refrigerants at an accelerated pace due to the

fast approaching deadlines set by the Montreal Protocol and subsequent Kigali agreement. Ammonia,

one such natural refrigerant, has been widely used for decades but is also being burdened with

increased regulation since traditional refrigeration systems utilizing central machine rooms require such

large ammonia quantities. However, the benefits of ammonia cannot be dismissed. Within the last five

years, a stronger focus has been on the development of industrial low charge ammonia packaged

refrigeration systems for industrial refrigeration similar to how halocarbon based packaged refrigeration

systems have evolved in the commercial industry. What has been critically dismissed in pursuing

systems with ‘ultra-low charge’, in some cases, is reliability and efficiency. Achieving ultra-reliable,

efficient operation with low ammonia charge is the key to success for low charge ammonia packaged

refrigeration systems.

Executive Summary

In the United Sates, increasing regulations directed towards owners of large ammonia systems has

resulted in higher operating cost and increased liability. In response, many owners, particularly in the

cold storage market segment are demanding low charge systems. Low charge ammonia caught the

attention of equipment manufacturers and engineers in the industrial refrigeration industry. The phrase

“low charge” is immediately interpreted to mean “as efficient as” and “safer than” a traditional central

machine room system. However, two other aspects that are just as, or more, critical are the ultra-

reliable operation and meeting the stated refrigeration capability. Ultra-reliable operation, as

established by Evapco for packaged low charge ammonia refrigeration systems, is the safe, consistent

and stable startup, operation and shutdown at all load and ambient conditions.

During the early development, Evapco approached low charge ammonia packaged system design too

aggressively trying to apply innovative new concepts to the system design and controls to meet the

‘ultra-low charge’ claims of some other manufacturers. The ‘ultra-low charge’ numbers promoted were

less than one pound of ammonia per ton of refrigeration for direct air-cooling penthouse systems and

ounces of ammonia per ton of refrigeration for chillers, or secondary non-volatile fluid refrigeration

systems.

As is customary in developing any product, Evapco performs extensive testing on full scale products. This

testing provides valuable information into how low charge ammonia systems operate differently than a

traditional system. These packages are new systems that behave differently due to the dynamic


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operation created by close coupled components. The odds of successfully producing a packaged low

charge ammonia refrigeration system simply by assembling smaller sized components used in a

traditional system design is highly improbable. Thorough testing of these systems through a wide range

of operating conditions proved numerous factors will affect a packaged refrigeration system thermal

capability, amount of charge required, efficiency and reliability. These factors include the close-coupled

package arrangement, system feed type, condensing method, ambient temperatures, room application

temperature, component commercialization, load variations, oil management and even designing to

comply with building codes.

Testing confirmed the amount of refrigerant charge needed to operate at a full load and design

temperatures is different than the charge required to operate at part load and/or low ambient

temperatures. Based on Evapco’s extensive research and testing, it seems some manufacturers claimed

charge required for and thermal capacity of their packaged ammonia refrigeration systems don’t take

into account the wide range of conditions the package will be subjected to during actual operation.

Only after reliable operation is established can meaningful values for the actual thermal capability,

efficiency, CoP and ammonia charge be determined. The purpose of this paper is to present some

findings during design and testing that led to the development of fully rated packaged low charge

ammonia refrigeration systems.

Design Considerations

The close-coupled, compact nature of a packaged system is a primary driving factor in reducing overall

refrigerated facility ammonia charge compared to a conventional central machine room design that uses

long pipe runs to transfer ammonia through the closed system. This benefit of reduced ammonia charge

for packaged systems does not come without its challenges. Low charge system operation is much more

dynamic and requires control systems which are more responsive as these systems do not have the

ballast of large ammonia charges and long pipe runs to ‘dampen’ upset conditions. It became clear that

applying a conventional refrigeration system design and standard control logic is not a ‘copy-paste’

undertaking for low charge packaged refrigeration systems.

System Type, Condensing Method, and other Components

The primary influence which impacts total ammonia charge is the type of system. Aside from systems

using a non-volatile secondary circuit, direct expansion (DX) systems are widely thought to be the only

means of achieving low charge. Compared to traditional recirculated liquid systems that operated at up

to 4:1 recirculation rates, that perception would be true. However, tube and fin evaporator coil

technology has improved where optimum thermal capability occurs at recirculation rates of 1.1:1 or

1.2:1. As a result, the ammonia charge per ton of refrigeration of a recirculated liquid coil operating at

1.2:1 can be equal to or better than that of a DX coil. This technology improvement provides

opportunity for significant charge reduction in the evaporator and through reduced piping and

component size of pumped liquid systems.

Another factor influencing the charge required packaged refrigeration system charge is the type of

condenser used; air-cooled or water-cooled. Water-cooled condensing systems will generally require

less charge than air-cooled condensing systems due to their higher heat transfer coefficients and lower

volume. In addition, oil temperature control, compressor differential pressure control and freezing

effects need to be considered for proper operation at off-design low ambient temperature conditions.


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However, each of these issues can be managed with proper control of the water supply temperature

and flow rate to maintain minimum condensing temperatures.

Air-cooled condensing systems require additional considerations to properly manage liquid ammonia in

the system during periods of shutdown. Similar to a water-cooled condenser, oil temperature control

and compressor differential pressure control are major issues associated with startup of an air-cooled

condensing system driven by the over-performance of the air-cooled condenser resulting from high

temperature differentials between minimum condensing temperature and very low-ambient conditions.

The emphasis on designing ultra-low charge packaged systems by reducing the size of key system

components can inadvertently complicate and limit system operation. For example, vessels are

traditionally larger volume for conventional central machine room systems that utilize long pipe runs to

store the ammonia charge surges. In a close-coupled package system with short pipe runs, the surge

volume and vessel size can be significantly reduced.

Efficiency

System designers and purchases should not evaluate low charge packaged systems on refrigerant charge

only. The packaged system efficiency and coefficient of performance (CoP) are equally important. The

design of the low charge system, recirculated liquid versus DX, and type of condenser used result in a

wide range of charge values and installed power for a specified heat rejection capability The efficiency

and CoP of the packaged system must be taken into account during the design phase with primary

consideration directed toward the efficiency of key components – compressor and motor, pump (if

recirculated liquid), evaporator fans, condenser fan or fluid cooler or cooling tower. The system’s

control logic also impacts overall system efficiency. The use of variable frequency drives (VFD), slide

valve control and economized system design will positively influence the efficiency of the system, if

properly applied. As an example, applying speed control to evaporator fans can increase the CoP at part

load operation but may not provide adequate airflow to a particular room.

Another important consideration is the total efficiency of the refrigerated facility. The use of multiple

packaged systems on a refrigerated facility, referred to as distributed refrigeration, is often more

efficient than a central machine room system when taking into account the reduced pressure drop

(elimination of long pipe runs), system suction temperatures matched to each room’s application

temperature, and more prevalent use of VFD’s.

Installation

Consideration must also be extended to the installation requirements of each system. Air-cooled

condensing systems requiring only electrical utilities offer simpler installations in exchange for increased

charge and energy consumption. Water-cooled condensing systems reduce charge and energy

consumption for the same refrigeration capability but also require water, water treatment and

additional maintenance attributed to evaporative cooled products.

Codes

As previously mentioned, codes and regulations applicable to ammonia systems have changed

considerably over the last five years. Complying with these codes and regulations can influence system

design and complicate system operation. However, applying factory assembled low charge package

systems designed and built to be in accordance with established codes and standards can reduce the

impact of regulations due to the low ammonia charge associated with each isolated system.


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The Metrics

When developing a low charge ammonia packaged refrigeration system, attention is directed toward

limiting the total charge quantity per system (i.e., 500 lbs satisfying IIAR’s new Low Charge Ammonia

Response Management guidelines) or charge per ton, CoP, and the installed cost of the unit. However,

these metrics get influenced by the unique operational challenges associated with achieving ultra-

reliable operation for each system feed, condensing method and room application temperature.

Evapco’s test results have proven that operating packaged systems at ultra-low refrigerant charge is

possible, but only for a limited range of operating conditions. Some of these ultra-low charge systems do

not provide the refrigeration capacity and/or system efficiencies when operating outside a limited range

of conditions. This issue can lead some to conclude low charge systems are not a viable solution for

refrigerated facilities. Ultra-reliable, safe and efficient operation of a packaged low charge ammonia

system can be achieved through thorough testing at a wide range of conditions.

Testing Facilities

Testing is a fundamental requirement to researching and developing fully rated packaged low charge

ammonia refrigeration systems that are ultra-reliable and efficient. During the last five years, Evapco has

performed numerous laboratory tests on multiple full-scale systems at its Research Center in

Taneytown, MD (USA). The facilities at Evapco’s disposal have been instrumental in gathering technical

data related to system operation and the development of system controls to effectively manage the

ammonia at conditions enveloping a wide range of load and ambient conditions. These facilities are

described below to support the discoveries and data presented later in the paper.

Low Temperature Environmental Chamber

The first packaged low charge ammonia refrigeration system prototyped by Evapco was a recirculated

liquid system utilizing air-cooled condensing. This unit was tested in Evapco’s Low Temperature

Environmental Chamber [Fig. 1] to research how the system would be affected while operating in

climates with extremely low ambient temperatures. The test chamber is designed similar to a

refrigerated warehouse with a fully functioning ammonia refrigeration system, insulated walls and

ceiling, and underfloor heating. This test chamber is normally used for testing Evapco’s forced air fin and

tube evaporators and is capable of producing room temperatures as low as -40 °C [-40 °F]. In this case,

the chamber created the ambient conditions for testing the packaged low charge ammonia refrigeration

system prototype. The first prototype unit was tested at ambient dry bulb temperatures ranging from -

23 °C to 38 °F [-9 °F to 100 °F] measuring thermal capability and observing system operation. Testing

packaged systems in this chamber was limited in both size and time available. Evapco decided to design

and install a test stand dedicated to testing packaged low charge ammonia refrigeration system.


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Test Stand

In 2015, Evapco designed and installed a dedicated test stand suitable for testing a multitude of

packaged low charge ammonia refrigeration designs. The principle of operation is illustrated in Figure 2.

The tested unit sits over a Test Plenum Heat Coil section (C). The fans in the penthouse section (B)

recirculate air through the evaporator coils in the penthouse section where heat is rejected and the Test

Plenum Heat Coil section where heat is introduced to simulate the system load. When testing water-

cooled condensing systems, the heat load provided to the Test Plenum Heat Coils comes from the water

absorbing the heat from the water-cooled condenser. An alternate boiler loop (D) is the heat source of

the test plenum heat coil section for testing systems utilizing air-cooled condensing. This test stand

allows Evapco to run various packaged low charge ammonia systems at various operating conditions.

The system’s refrigeration thermal capability is measured with abundant instrumentation. Temperature,

pressure, flow rate, liquid level and power of the unit, components and the test plenum section are

continuously recorded using RTD’s, pressure and liquid level transmitters and power meters to quantify

system performance and evaluate system operation. The accuracy of the instrumentation used results in

capacity tolerance less than 2 kilowatts [0.5 refrigeration tons] with a tolerance on system power of

±1%. Measurements and calculations of the air, refrigerant, and heat load are used for heat balance to

ensure accuracy of the test. The response of the control system and liquid management during part load

operation is evaluated by adjusting the amount of heat transferred to the Test Plenum Heat Coils.

Figure 1: Prototype in Low Temperature Environmental Chamber


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The only limitation of the test stand is the ability to control ambient temperature conditions. This is less

of an issue with water-cooled condensing systems for several reasons. First, it is easier to maintain the

minimum condensing temperature of the system through water supply temperature and flow rate

manipulation at low ambient temperatures. Additionally, the water-cooled plate and shell condenser

usually has less charge than an equivalent air-cooled condenser and is located in the temperature-

controlled machine room. However, air-cooled condensing systems are more influenced by the ambient

conditions for the opposite reasons. The air-cooled condenser is outside and directly affected by the

ambient temperatures. Furthermore, air-cooled condensers generally require more surface, volume and

charge due to lower heat transfer coefficients compared to water-cooled condensers. These factors add

to the challenge of ultra-reliable operation over the wide range of real-world conditions. In order to

evaluate air-cooled condensing systems thoroughly, a low temperature environment needed to be

created to evaluate system operation.

Low Ambient Temperature Testing

Evapco’s first packaged low charge ammonia refrigeration system prototype was tested in the Low

Temperature Environmental Test Chamber normally used for testing fin and tube evaporators. This

chamber is not large enough to test larger penthouse packages routinely tested on the test stand.

Fortunately, Evapco found a supporting partner in Creative Thermal Solutions, Inc. (CTS) to test larger

packaged low charge ammonia refrigeration systems utilizing air-cooled condensing. CTS adapted one of

its buildings to accommodate indoor testing of a full-scale air-cooled condensing packaged penthouse

A B

C

D

Figure 2: Packaged Ammonia Refrigeration System Test Stand


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refrigeration system at extremely low ambient conditions similar to the Low Temperature

Environmental Test Chamber. A representation of the unit in the chamber is shown in Figure 3 and an

image of the air-cooled condenser installation in the test chamber is shown in Figure 4.

The entire building was insulated to maintain a -23 °C [-9 °F] ambient temperature. The fans in the

penthouse circulated the air through an isolated tunnel. Within the tunnel, air passed through the

evaporator coils where heat was rejected, through an AMCA style nozzle wall for airflow measurement

and finally through a set of heat coils where heat was added back into the air. Measurements on the

circulated air and refrigeration system provided accurate load calculations for efficiency and CoP

calculations. Additional testing was performed to evaluate startup and shutdown sequences for reliable

operation.

Observations from Testing

The first packaged low charge ammonia refrigeration system prototype became the benchmark for

understanding the need for and importance of ultra-reliable operation. Focused on reducing charge to

the lowest possible level and eager to bring something new and innovative to the refrigeration industry,

new technologies and innovations were implemented in the design. Unfortunately, some of the new

packaged technologies and innovations attempted in the original prototype were discovered through

testing to only be effective for limited operating conditions. Introducing a low charge product with

limited reliability and flexibility to operate over the range of conditions known to exist in a traditional

refrigeration facility would have been detrimental to the public’s perception of packaged low charge

ammonia refrigeration systems. It became clear that starting with a more conventional system design

and observing how this system would be affected by the dynamic nature of the smaller packaged system

was prudent. Testing this air-cooled condensing system prototype in the Low Temperature

Environmental Test Chamber also validated the need to test multiple units at a wide range of load and

ambient conditions.

Lastly, another important discovery was made during testing of the first prototype. While rarely

mentioned or even suggested, commercialism of product thermal capacity and energy use exists at

Figure 3: Model of Low Ambient Test Chamber for

Air-Cooled Condensing Packaged System Testing

Figure 4: Condenser Installation in Low Ambient Test

Chamber


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various levels in the refrigeration industry supply chain. This commercialism is routinely accepted and

accounted for through safety factors and conservative “rules of thumb” when calculating loads. This is

an obstacle when designing and developing a fully rated product line of packaged refrigeration systems.

The design of the first prototype fell short of achieving the expected thermal capability due to the

inability of components to achieve 100% of the stated capacity. Reliable and consistent startup and

shutdown sequences were also not achieved. Validating the capability of each component became

necessary to understand how to adjust manufacturer’s claimed performance in order to determine

capacity of the packaged system as a whole. Because of strong supply chain relationships, the

information obtained from testing was shared and discussed with component manufacturers.

Once the above obstacles were overcome, the operation of prototype systems became more reliable.

However, we identified other obstacles, primarily at part load and low ambient temperature conditions.

These obstacles included oil temperature control, compressor differential pressure control, freezing

effects for water-cooled condensing systems, and liquid ammonia management.

Compressor Differential Control – Hot/Cold Starts

Particularly challenging to the reliable operation of packaged ammonia refrigeration systems is

compressor differential control for hot and cold starts. The most adverse hot start occurs during initial

commissioning of the cold storage warehouse or after long term shut-downs. Commissioning can occur

during the hottest days of summer when suction and discharge pressures are very high due to high

temperature differentials across the evaporator and high condensing temperatures due to high ambient

temperatures. Additionally, commissioning is most often conducted under part-load operation which

takes time to reduce suction temperature and pressure. This situation was replicated during laboratory

testing when the compressor cycled off failing to achieve differential pressure and sufficient oil pressure

before the time delay expired. This scenario was overcome by closing the compressor suction valve to

artificially reduce the suction pressure and increase the differential pressure. As the room temperature

reduced, the suction valve was opened or bypassing load.

It was observed during testing that cold starts pose more difficult challenges than hot starts. Low

ambient temperatures significantly lower the ammonia condensing temperature. Consequently, this

reduces the saturation condensing pressure and differential pressure below the minimum required for

compressor startup and operation. In a water-cooled condensing system, the cooling fluid temperature

can be managed to a minimum temperature or flow reduced to allow the ammonia condensing

temperature to increase to satisfy the compressor differential pressure requirement.

Oil System Control

Oil temperature control is vital to the proper operation of the system and the longevity of the

compressor. Excessive oil temperatures can lead to premature compressor bearing and compressor

shaft seal failures. These particular packaged ammonia refrigeration systems do not include oil pumps.

Oil flow is generated from the pressure differential created between the compressor discharge and

suction pressure. Therefore, maintaining compressor differential is essential to the proper operation of

the compressor oil system.

During normal operation, controls are in place to ensure the required compressor differential is

maintained including discharge pressure control based on condenser water control, suction temperature

control based on compressor speed or on/off cycling, and oil differential pressure control safeties.


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However, oil temperature control for water-cooled systems is different than air-cooled condenser

systems. In this case, the oil cooler in a water-cooled packaged refrigeration system is integrated with

the plate and shell condenser. Oil temperature can be easily maintained by controlling the water

temperature or flow rate from the open or closed-circuit cooling tower through tower fan speed, pump

speed or bypass.

The oil cooler in an air-cooled packaged refrigeration system is a thermosyphon plate and shell heat

exchanger. Challenges with startup were encountered during low ambient conditions when oil is cooler

than normal operation. To provide reliable startup under these conditions, a 3-way valve was

implemented to allow mixing of the oil during start-up operations. The 3-way valve also allows better

control and balancing of oil temperatures. The hot oil then travels to the heat exchanger and is cooled.

The cooled oil returns to the compressor and recycled to maintain a constant acceptable oil operating

temperature.

Cold start operation is more complicated for an air-cooled condensing refrigeration package. Oil

temperature and compressor differential pressure control issues at start-up are driven by the over-

performance of the air-cooled condenser at very low ambient conditions. Reducing condenser oil

surface, modulating condenser fans and regulating ammonia gas flow were all discovered in testing to

be viable means of countering air-cooled condenser over-surface at low ambient conditions.

In addition to the oil temperature and compressor differential pressure control issues of a water-cooled

system, liquid migration during shutdown of an air-cooled condensing system becomes another issue.

Large temperature gradients can occur between the air-cooled condenser located outside, the

components of the machine room located in a heated space and the evaporator coils subject to the

room application temperature. As a result, liquid ammonia can migrate to different locations reducing

liquid volume in vessels needed for pump operation. Therefore, vessels and other components must be

sized to contain the varying charge levels in the system and require an increase in the overall system

charge to ensure ultra-reliable operation.

Several control schemes were tested to maintain the required compressor differential and appropriately

manage the liquid ammonia. Interestingly, different control components and control schemes could be

employed for different room application temperatures. Isolation of the ammonia within the system is

also a consideration. Precautions must be taken to prevent hydrostatic isolation.

Referring to the first prototype tested in the Low Temperature Environmental Chamber, as the ambient

temperature was reduced and heat load was removed replicating part load low ambient operation,

system operation from start-up to shutdown became more erratic. This was attributed to inadequate

liquid ammonia management. The air-cooled condenser was subjected to the ambient temperature, the

compressor and vessels were in a machine room that is heated to maintain a minimum temperature and

the penthouse was exposed to the cold storage / process temperature. As a result, liquid ammonia

migrated out of the machine room to colder locations of the system. It was concluded that managing

where the liquid is in a packaged system is very important. Vessels and systems must be sized to contain

the various charge levels through start-up, operation and shutdown at all possible load and ambient

conditions. The testing at CTS revealed additional information that different methods of ammonia

migration control could be implemented effectively depending on the room application and ambient

temperatures.


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Efficiency

After achieving ultra-reliable operation and the resulting ammonia charge that supports it, attention is

directed to optimizing CoP. The packaged low charge ammonia refrigeration systems discussed in this

paper utilize screw compressors which are commonly chosen for cold storage warehouse designs based

on tonnage, low saturated suction conditions, operational flexibility and convenience for incorporating

into a compact design.

Several options can also

be employed to improve

efficiency part-load

operation. Through

testing, a combination of

both speed and slide valve

control was identified to

yield better CoP’s at part

load operation as shown

in Figure 5. Multiple

packaged systems on a

refrigeration facility can

provide improved

efficiency and additional

energy savings by cycling

off when room conditions

are met.

At lower saturated suction temperatures, compressor efficiency can be increased by utilizing an

economized cycle improving CoP 5-10%. The trade-off of using an economized cycle for CoP

improvements is the need for an additional vessel which increases ammonia charge. The additional

vessel and increased ammonia charge is generally not warranted at higher suction temperatures since

an improvement like this is not realized to this extent.

Another consideration for improving the CoP of the system at part load operation is implementing

speed control on the evaporator fans. However, not all applications can operate with reduced fan speed

due to air throw and minimum required air changes based on product cooling requirements. How the

fan speed is controlled as well as how multiple packaged refrigeration systems are arranged on the

facility greatly influences this opportunity.

There are some key energy efficiency advantages of multiple packaged low charge ammonia systems,

distributed systems, compared to central machine room systems. Distributed system packaged units

eliminate the energy-consuming piping pressure drop of long piping runs common with traditional

central machine room systems. Typical piping runs for central machine room systems can add up to 2 °C

to 3°C [3° to 5°F] to the saturation temperature from system pressure losses, forcing the central

machine room compressors to operate at lower suction pressures to overcome the losses and

consuming additional energy.

Distributed system packaged units allow the refrigerant suction temperatures to be matched precisely

and continuously to each individual room temperature, allowing each room to operate as efficient as

Figure 4: Compressor Efficiency - Speed and Slide Valve Control


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possible, versus a traditional central machine room system that is typically limited to only 2 or 3 “house

suction” temperatures, which serve many rooms and many room temperatures.

Distributed units commonly have variable frequency drives included as standard for compressor control

allowing this primary energy user to operate very efficiently (Fig. 4). The smaller compressor motors in

Distributed Systems, versus central plant motors, allow VFD’s to be more commonly and cost effectively

applied. VFD’s can also be provided with the evaporator fans and condenser fans as well.

All of the above provide the ability for a facility to have a supervisory control system that provides

complete energy management at the point of use. Built-in software available in some Distributive

Systems, in conjunction with a supervisory control system, can provide very efficient energy

management.

Closing Comments

Ammonia is a very efficient and environmentally-friendly natural refrigerant. Evapco is committed to

developing product lines that support its continued safe use. Bold claims exist in the refrigeration

market for packaged ammonia systems that operate at miniscule amounts of ammonia. However, claims

only of low charge are meaningless without ultra-reliable and efficient operation and meeting stated

thermal and energy use capability. The purpose of this paper is to educate the refrigeration industry on

the challenges surrounding ultra-reliable, efficient, fully rated packaged low charge ammonia

refrigeration system design and present capability information gathered through extensive testing.

Table 1 below is a sample of the capacity and metrics for the packaged low charge ammonia

refrigeration systems tested and developed at the time of this paper. These numbers are reflective of

systems that:

• Will operate reliably at all load and ambient condition;

• Comply with the design requirements of IIAR-2; and

• Are fully rated

As expected, systems utilizing air-cooled condensing require more ammonia and consumer more energy

per ton of refrigeration and have slightly lower CoP’s than water-cooled systems at full load. However,

note that the values for water-cooled condensing systems do not account for external heat rejection

equipment including cooling towers and pumps. At some off-peak conditions, air-cooled condensing

systems can be as or more efficient. In comparing water-cooled condensing recirculated liquid systems

to DX systems, the charge is higher for about the same efficiency and CoP. However, comparing these

numbers to a conventional central machine room refrigeration system design is impractical since

accurate load calculation is nearly impossible to definitively know the actual tonnage capability of the

system. As mentioned previously, significant safety is typically included in traditional system design to

account for unknown heat loads and component capability commercialism that also clouds the true

system operating capacity. Conventional central machine room refrigeration systems are estimated to

require 15-30 pounds of ammonia per ton of refrigeration so there is clearly a significant charge

reduction in packaged ammonia refrigeration systems. In addition, multiple packaged refrigeration

systems can also offer improved efficiency and redundancy. Most importantly, when designed

appropriately and tested thoroughly, packaged ammonia refrigeration systems will provide ultra-reliable

operation.


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Table 1: Package Low Charge Ammonia Refrigeration System Metrics

System Type Cond

Type

Room

Temp

Average Metrics at Maximum Capacity

kW [TR] kg/kW [lb/TR] kW/kW* [hp/TR]* COP*

LCR-LR-P-SC Air Low 211 [60] 1.06 [8.2] 0.74 [3.5] 1.4

LCR-LR-P-SC Air Med 246 [70] 0.90 [7.0] 0.52 [2.5] 1.9

LCR-LR-P-SC Air High 264 [75] 0.69 [5.4] 0.45 [2.1] 2.2

LCR-LR-P-SC Water Low 211 [60] 0.70 [5.4] 0.43 [2.0] 2.3

LCR-LR-P-SC Water Med 317 [90] 0.54 [4.2] 0.30 [1.4] 3.4

LCR-LR-P-SC Water High 352 [100] 0.41 [3.2] 0.22 [1.0] 4.6

LCR-LR-P-DC Water Low 211 [60] 0.70 [5.4] 0.46 [2.2] 2.2

LCR-LR-P-DC Water Med 371 [105] 0.54 [4.2] 0.29 [1.4] 3.5

LCR-LR-P-DC Water High 352 [100] 0.42 [3.3] 0.27 [1.3] 3.6

LCR-DX-P-SC Water Med 317 [90] 0.36 [2.8] 0.30 [1.4] 3.3

LCR-DX-P-SC Water High 352 [100] 0.25 [2.0] 0.22 [1.0] 4.5

LCR-C-SC Water Med 454 [129] 0.11 [0.9] 0.28 [1.3] 3.5

LCR-C-SC Water High 475 [135] 0.11 [0.8] 0.25 [1.2] 3.9

LCR-C-SC Water Med 1125 [320] 0.10 [0.8] 0.24 [1.1] 4.2

LCR-C-SC Water High 1382 [393] 0.08 [0.6] 0.18 [0.9] 5.5

LCR ≡ Packaged Low Charge Refrigeration LR ≡ Recirculated Liquid Penthouse

SC ≡ Single 100% Compressor DX ≡ Direct Expansion (DX) Penthouse

DC ≡ Dual 50% Compressors C ≡ Chiller

*Water-cooled condensing systems do not include cooling tower fans or pumps for heat rejection.

Research and development will continue with respect to packaged low charge ammonia refrigeration

systems including direct expansion (DX) systems and expanded use of air-cooled condensing systems.

New concepts and innovations are being developed that, when applied to these first-generation low

charge packaged systems, will improve the metrics illustrated above promoting the continued and

expanded safe and efficient use of ammonia.

Acknowledgements

Dr. Pega Hrnjak, Art Marshall, Brian Marriott, Creative Thermal Solutions, Inc., AAIM Controls, Inc.

References

Low Charge Ammonia Refrigeration Management (ARM-LC) Guidelines, 1st edition.

low charge ammonia packaged refrigeration systems ......the first packaged low charge ammonia...

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